Multiple sclerosis (MS) is a chronic, unpredictable disease of the central nervous system (CNS) where the body’s own immune system mistakenly attacks the protective layer, called myelin, surrounding nerve fibers. This damage disrupts the flow of electrical signals between the brain and the rest of the body. Because the CNS includes the brain, spinal cord, and the optic nerve, MS can affect nearly every bodily function, including the visual system.
The Direct Link: Optic Neuritis
The primary mechanism is a condition called Optic Neuritis (ON). This occurs when the immune system attacks the myelin sheath of the optic nerve, which is the bundle of fibers transmitting visual information from the eye to the brain. The resulting inflammation causes the nerve to swell and become damaged, directly impeding its function.
Demyelination slows or blocks the transmission of visual signals, causing temporary vision loss. This inflammation and swelling within the confined space of the optic nerve sheath is what triggers the pain. Optic neuritis is a common first clinical sign of MS for approximately 20% of patients, and almost half of all people with MS will experience it at some point in their disease course. The condition typically affects one eye at a time and can develop acutely over hours or days.
Characteristics of MS-Related Eye Pain
The pain often precedes or occurs concurrently with the onset of vision changes, such as blurring or color desaturation. It is frequently described as a deep, dull ache located behind or around the affected eye.
A hallmark feature of this pain is that it significantly worsens with eye movement. Simple actions like looking up, down, or to the side can exacerbate the discomfort because the movement stretches the inflamed and swollen optic nerve. Around 90% of people experiencing optic neuritis report this eye pain, which can sometimes radiate to the surrounding areas or present as a headache at the front of the head.
Other Vision Symptoms Caused by MS
While optic neuritis is the main cause of eye pain in MS, the disease can cause other vision issues that are not characterized by pain. These other symptoms result from lesions in different parts of the CNS, such as the brainstem, which controls eye movement coordination. One common issue is diplopia, or double vision, which occurs because the muscles of the eyes are no longer working together.
Another frequently observed symptom is nystagmus, which involves rapid, involuntary movements of the eyes. This can cause a sensation of the world jumping or swaying, sometimes leading to dizziness. Double vision and nystagmus are often caused by damage to the pathways that control the synchronicity of eye movements, such as in a condition called internuclear ophthalmoplegia.
Diagnosis and Management of Eye Pain
When a patient presents with sudden eye pain and vision changes, a prompt medical evaluation is necessary to confirm optic neuritis and rule out other potential causes. The diagnostic process typically involves a thorough ophthalmological examination, including tests for visual acuity, color vision, and a check for a relative afferent pupillary defect. This specific defect shows the affected eye’s pupil reacting less vigorously to light compared to the unaffected eye.
Magnetic Resonance Imaging (MRI) is a key tool, allowing doctors to look for signs of inflammation and swelling in the optic nerve itself. An MRI of the brain is also performed to check for other lesions characteristic of MS. Another test, the Visual Evoked Potential (VEP), measures the speed of electrical signals traveling from the eye to the visual cortex of the brain.
Management for acute optic neuritis often involves high-dose intravenous corticosteroids, such as methylprednisolone, administered over three to five days. Steroids work by suppressing the immune system and reducing the inflammation and swelling of the optic nerve, which can speed up the recovery of vision. While steroids accelerate the resolution of the episode, they do not ultimately change the long-term visual outcome, as most people recover partial or full vision even without treatment.